The determination of a moment of impact using an acceleration sensor is important for certain applications including automotive crash protection using one or more airbags which must be deployed promptly after impact to limit personal injury of an automobile's occupants. Acceleration sensing devices formed by silicon micromachining have been disclosed (see e.g. U.S. Pat. No. 6,199,874). These acceleration sensing devices, which have been formed as microelectromechanical (MEM) devices, generally utilize a structure having a plurality of interdigitated fingers for determining changes in acceleration due to a change in capacitance upon movement of the interdigitated fingers. No latching capability is provided in such devices.
The present invention represents an advance over the prior art by providing an acceleration-sensing apparatus which has a latching capability for sensing the occurrence of an acceleration component and then permanently completing an electrical circuit to indicate the occurrence of the acceleration component.
The acceleration-sensing apparatus of the present invention does not sense small changes in acceleration, but rather senses the occurrence of an acceleration component directed along an axis of the device which exceeds a predetermined acceleration threshold (e.g. due to an impact). Once the predetermined acceleration threshold is sensed, the apparatus of the present invention is permanently latched until mechanically released to provide an electrical switch closure that can be used for the activation of certain peripheral devices (e.g. an electronic control unit for igniting a gas generator for inflating an airbag) used in conjunction with the acceleration-sensing apparatus.
The acceleration-sensing apparatus of the present invention can be formed as a uni-directional or bi-directional device. Additionally, certain embodiments of the acceleration-sensing apparatus of the present invention can be utilized to sense the occurrence of multiple acceleration events separated in time.
These and other advantages of the present invention will become evident to those skilled in the art.